Cryptography is the art to exchange information between a sender (“Alice”) and a receiver (“Bob”), rendering it unintelligible to any other person. A readable text is encrypted with a secret key through an algorithm by Alice and then sent to Bob that can recover the plain text using a decryption algorithm and the secret key. The “key distribution problem” is fundamental in information exchange security. This problem has been solved by “public key cryptography” based on one-way functions. However, even if reversing one-way functions is an extremely time consuming task, future computers could become fast enough to crack the key in a reasonable time or mathematics progress could find the existence of algorithms that allow reversing one-way functions. Security of key transmission depends on: key length, key change frequency and method to protect key exchange (true random numbers generation and chance for an intruder, “Eve”, to intercept the key).
Quantum Key Distribution (QKD) is one way to solve this problem having Heisenberg's uncertainty principle as guarantee. In QKD encoding of each bit (“qubit”) is done on the property of a photon (e.g. polarization, phase): any tentative by Eve to intercept bits of the key will cause perturbation and errors in the sequence of bits, detected by Alice and Bob. So “a posteriori”, only if the key has not been intercepted can be validated to encrypt data (e.g. monitoring BER change compared to a reference). QKD and quantum (true) random numbers generation with key refresh rate, at least, once per second make truly secure data encryption. QKD doesn't want to replace existing encryption technologies (e.g. SSL, Public Key Infrastructure), but is applied mainly as combination of QKD and classical data encryption to ensure, if needed, a totally safe information exchange. Main applications could be: financial information and trading exchange, Storage Area Networks, Point-to-point links with extremely high security level.
Players in QKD field are mainly focused to solve the problem of the single photon or weak light pulses transmission/detection technology and how to carve “qubits” on photons in a stable and reliable way. However, existing QKD structures do not consider integration in optical systems architectures (e.g. DWDM systems). In DWDM optical systems, the Optical Service Channel (OSC) is usually designed for span-by-span transmission of service information between any two adjacent sites.
Others have developed structures based on quasi-single photon transmission/detection where, as example, the key distribution is accomplished through an optical distributed Mach-Zender circuit adopting: a single wavelength bi-directional configuration or a mono-directional configuration operating at 1300 nm (reference clock laser) and 1550 nm wavelengths. However, these solutions use a second optical fiber for real traffic channels due to optical crosstalk problem over the quantum channel operating at very low power.
Therefore, a need exists for a method for integrating OSC and QKD onto one optical fiber to optimize performance (i.e. reducing the impact of real traffic optical channels crosstalk on quantum key distribution channel) and to reduce costs (e.g. using one optical fiber for traffic and key distribution). A primary purpose of the present invention is to solve these needs and provide further, related advantages.